Over 12 million people around the world suffer from Congestive Heart Failure (CHF). This is a family of related conditions defined by the failure of the heart to pump blood efficiently resulting in congestion (or backing up of the blood) in the lungs or peripheral circulation. CHF can ultimately lead to end-organ failure, which contributes to death of the patient. The heart muscle of the CHF patient may be altered with the chambers dilated and the heart walls thickened or thinned. CHF can result from several conditions, including infections of the heart muscle or valve, physical damage to the valve or by damaged muscle caused by infarction (heart attack).
CHF is the fastest-growing cardiovascular disease with over 1 million new cases occurring each year. Conservative estimates suggest that the prevalence of CHF will more than double by 2007. If untreated, CHF may result in severe lifestyle restrictions and ultimately death. One of the causes of CHF and a very common contributor to the harmful effects of CHF is a leaky mitral heart valve. The mitral valve is located in the center of the heart between the two left or major heart chambers and plays an important role in maintaining forward flow of blood. The medical term for this leaky condition is “mitral regurgitation” and the condition affects well over one million people globally. Mitral regurgitation is also called ‘mitral incompetence’ or ‘mitral insufficiency’.
For general background information, the circulatory system consists of a heart and blood vessels. In its path through the heart, the blood encounters four valves. The valve on the right side that separates the right atrium from the right ventricle has three cusps and is called the tricuspid valve. It closes when the ventricle contracts during a phase known as systole and it opens when the ventricle relaxes, a phase known as diastole.
The pulmonary valve separates the right ventricle from the pulmonary artery. It opens during systole, to allow the blood to be pumped toward the lungs, and it closes during diastole to keep the blood from leaking back into the heart from the pulmonary artery. The pulmonary valve has three cusps, each one resembling a crescent and it is also known as a semi-lunar valve.
The two-cusped mitral valve, so named because of its resemblance to a bishop's mitre, is in the left ventricle and it separates the left atrium from the ventricle. It opens during diastole to allow the blood stored in the atrium to pour into the ventricle, and it closes during systole to prevent blood from leaking back into the atrium. The mitral valve and the tricuspid valve differ significantly in anatomy. The annulus of the mitral valve is somewhat D-shaped whereas the annulus of the tricuspid valve is more nearly circular.
The fourth valve is the aortic valve. It separates the left ventricle from the aorta. It has three semi-lunar cusps and it closely resembles the pulmonary valve. The aortic valve opens during systole allowing a stream of blood to enter the aorta and it closes during diastole to prevent any of the blood from leaking back into the left ventricle.
In a venous circulatory system, a venous valve functions to prevent the venous blood from leaking back into the upstream side so that the venous blood can return to the heart and the lungs for blood oxygenating purposes.
Clinical experience has shown that repair of a valve, either a heart valve or a venous valve, produces better long-term results than does valve replacement. Valve replacement using a tissue valve suffers long-term calcification problems. On the other hand, anticoagulation medicine, such as cumadin, is required for the life of a patient when a mechanical valve is used in valve replacement. The current technology for valve repair or valve replacement requires an expensive open-heart surgery that needs a prolonged period of recovery. A less invasive or catheter-based valve repair technology becomes an unmet clinical challenge.
The effects of valvular dysfunction vary. Mitral regurgitation may have more severe physiological consequences to the patient than does tricuspid valve regurgitation. In patients with valvular insufficiency, it is an increasingly common surgical practice to repair the natural valve, and to attempt to correct the defects. Many of the defects are associated with dilation of the valve annulus. This dilatation not only prevents competence of the valve but also results in distortion of the normal shape of the valve orifice or valve leaflets. Remodeling of the annulus is therefore central to most reconstructive procedures for the mitral valve.
As a part of the valve repair it is either necessary to diminish or constrict the involved segment of the annulus so that the leaflets may coapt correctly on closing, or to stabilize the annulus to prevent post-operative dilatation from occurring. The current open-heart approach is by implantation of a prosthetic ring, such as a Cosgrove Ring or a Carpentier Ring, in the supra annular position. The purpose of the ring is to restrict and/or support the annulus to correct and/or prevent valvular insufficiency. In tricuspid valve repair, constriction of the annulus usually takes place in the posterior leaflet segment and in a small portion of the adjacent anterior leaflet.
Various prostheses have been described for use in conjunction with mitral or tricuspid valve repair. The ring developed by Dr. Alain Carpentier (U.S. Pat. No. 3,656,185) is rigid and flat. An open ring valve prosthesis as described in U.S. Pat. No. 4,164,046 comprises a uniquely shaped open ring valve prosthesis having a special velour exterior for effecting mitral and tricuspid annuloplasty. The fully flexible annuloplasty ring could only be shortened in the posterior segment by the placement of plicating sutures. John Wright et al. in U.S. Pat. No. 5,674,279 discloses a suturing ring suitable for use on heart valve prosthetic devices for securing such devices in the heart or other annular tissue. All of the above valve repair or replacement requires an open-heart operation which is costly and exposes a patient to higher risk and longer recovery than a catheter-based, less invasive procedure.
Moderate heat is known to tighten and shrink the collagen tissue as illustrated in U.S. Pat. No. 5,456,662 and U.S. Pat. No. 5,546,954. It is also clinically verified that thermal energy is capable of denaturing the tissue and modulating the collagenous molecules in such a way that treated tissue becomes more resilient (“The Next Wave in Minimally Invasive Surgery” MD&DI pp. 36–44, August 1998). Therefore, it becomes imperative to treat the inner walls of an annular organ structure of a heart valve, a valve leaflet, chordae tendinae, papillary muscles, and the like by shrinking/tightening techniques. The same shrinking/tightening techniques are also applicable to stabilize injected biomaterial to repair the defect annular organ structure, wherein the injectable biomaterial is suitable for penetration and heat-initiated shrinking/tightening.
One method of reducing the size of tissues in situ has been used in the treatment of many diseases, or as an adjunct to surgical removal procedures. This method applies appropriate heat to the tissues, and causes them to shrink and tighten. It can be performed in a minimal invasive or percutaneous fashion, which is often less traumatic than surgical procedures and may be the only alternative method, wherein other procedures are unsafe or ineffective. Ablative treatment devices have an advantage because of the use of a therapeutic energy that is rapidly dissipated and reduced to a non-destructive level by conduction and convection, to other natural processes.
Radiofrequency (RF) therapeutic protocol has been proven to be highly effective when used by electrophysiologists for the treatment of tachycardia, atrial flutter and atrial fibrillation; by neurosurgeons for the treatment of Parkinson's disease; by otolaryngologist for clearing airway obstruction and by neurosurgeons and anesthetists for other RF procedures such as Gasserian ganglionectomy for trigeminal neuralgia and percutaneous cervical cordotomy for intractable pains. Radiofrequency treatment, which exposes a patient to minimal side effects and risks, is generally performed after first locating the tissue sites for treatment. Radiofrequency energy, when coupled with a temperature control mechanism, can be supplied precisely to the device-to-tissue contact site to obtain the desired temperature for treating a tissue or for effecting the desired shrinking of the host collagen or injected bioresorbable material adapted to immobilize the biomaterial in place. Tweden, et al, in U.S. Pat. No. 6,258,122, entire content which are incorporated herein by reference, discloses that a bioresorbable heart valve annuloplasty prosthesis are eventually resorbed by the patient, during which time regenerated tissue replaces the prosthesis
Edwards et al. in U.S. Pat. No. 6,258,087, entire contents of which are incorporated herein by reference, discloses an expandable electrode assembly comprising a support basket formed from an array of spines for forming lesions to treat dysfunction in sphincters. Electrodes carried by the spines are intended to penetrate the tissue region upon expansion of the basket. However, the assembly disclosed by Edwards et al. does not teach a tissue-contactor member comprising a narrow middle region between an enlarged distal region and an enlarged proximal region suitable for sandwiching and compressing the sphincter for tissue treatment.
Tu in U.S. Pat. No. 6,267,781 teaches an ablation device for treating valvular annulus or valvular organ structure of a patient, comprising a flexible elongate tubular shaft having a deployable spiral wire electrode at its distal end adapted to contact/penetrate the tissue to be treated and to apply high frequency energy to the tissue for therapeutic purposes. Tu et al. in U.S. Pat. No. 6,283,962 discloses a medical ablation system for treating valvular annulus wherein an elongate tubular element comprises an electrode disposed at its distal section that is extendible from an opening at one side of the tubular element, the energy generator, and means for generating rotational sweeping force at the distal section of the tubular element to effect the heat treatment and the rotational sweeping massage therapy for target tissues. Both patents, entire contents of which are incorporated herein by reference, teach only the local tissue shrinkage, not for treating simultaneously a substantial portion of the valvular annulus.
U.S. Pat. No. 6,402,781 issued on Jun. 11, 2002, entire contents of which are incorporated herein by reference, discloses a mitral annuloplasty and left ventricle restriction device designed to be transvenously advanced and deployed within the coronary sinus and in some embodiments other coronary veins. The device places tension on adjacent structures, reducing the diameter and/or limiting expansion of the mitral annulus and/or limiting diastolic expansion of the left ventricle.
Hissong in U.S. Pat. No. 6,361,531 issued Mar. 26, 2002, entire contents of which are incorporated herein by reference, discloses focused ultrasound ablation device having malleable handle shafts. A remote energy source, such as ultrasound or microwave energy, can be emitted wirelessly to a focused target tissue located away from the ultrasound device. However, it is not disclosed for focused ultrasound energy for repairing a mitral valve or an atrioventricular valve annulus.
Therefore, there is a clinical need to have a percutaneous, or less invasive catheter or cannula-based approach as well as a surgical hand-held device for repairing an annular organ structure of a heart valve, a valve leaflet, chordae tendinae, papillary muscles, and the tissue defect by using high frequency energy (RF, microwave or ultrasound) for reducing and/or shrinking a tissue mass, with optionally an injected heat-shrinkable biomaterial along with the host tissue mass for tightening and stabilizing the dilated tissue adjacent a valvular annulus. There is also a clinical need for an improved apparatus system having capabilities of measuring a contact force at the point of contact with the tissue to be treated, as disclosed by one of inventors in U.S. Pat. No. 6,113,593, entire contents which are incorporated herein by reference.